The modification to an LM4 barrel is really easy. Its just taking a mill file to widen the two 'flats' on the barrel so that the hop up retension clip can snap back on. Took me about a minute for each side. I used an RA Tech TBB. I'm working on how to hide it now, but it shoots damn straight and easilly punches through both sides of an aluminum can from 20ft with .32 BBs. It will probably end up looking like a carbine version Kriss.

I wouldn't do it for someone... not enough experience with these things. It's my first airsoft gun on like ten years and my first time doing any modification. My old one is an old Tanaka H&K USP Heavy Weight. The manual says 1995, so it's really dated. I just followed BoobieM4H's video and it was easy.